(1) Field of the Invention
This invention relates generally to the control of plant pests and more particularly to the provision of protection against insect damage to seeds and plant parts by the treatment of plant seeds with combinations of pesticides; in particular, the invention relates to the control of insect damage to seeds and plant parts by the treatment of plant seeds with a combination of thiamethoxam with pyrethrins and/or synthetic pyrethroids.
(2) Description of the Related Art
The control of insects and related arthropods is of extreme importance to the agricultural industry. Every year, these pests destroy an estimated 15% of agricultural crops in the United States and even more than that in developing countries. Some of this damage occurs in the soil when plant pathogens, insects and other such soil borne pests attack the seed after planting. Much of the rest of the damage is caused by rootworms; plant pathogens that feed upon or otherwise damage the plant roots; and by cutworms, European corn borers, and other pests that feed upon or damage the above ground parts of the plant. General descriptions of the type and mechanisms of attack of pests on agricultural crops are provided by, for example, Metcalf, in Destructive and Useful Insects, (1962); and Agrios, in Plant Pathology, 3rd Ed., Academic Press (1988).
The period during germination of the seed, sprouting and initial growth of the plant is particularly critical because the roots and shoots of the growing plant are small and even a small amount of damage can kill the entire plant. Moreover, some natural plant defenses are not fully developed at this stage and the plant is vulnerable to attack. Not surprisingly, the control of pests that attack the seed and the above ground plant parts during this early stage of plant growth is a well developed area of agriculture.
Currently, the control of pests that attack post emergent crops primarily involves the application of synthetic organic pesticides to the soil, or to the growing plants by foliar spraying. Because of concern about the impact of chemical pesticides on public health and the environment, there has been much effort to reduce the amount of chemical pesticides that are used. A significant portion of this effort has been expended in developing transgenic crops engineered to express insect toxicants from microorganisms. For example, U.S. Pat. No. 5,877,012 to Estruch et al. discloses the cloning and expression of proteins from such organisms as Bacillus, Pseudomonas, Clavibacter and Rhizobium into plants to obtain transgenic plants with resistance to such pests as black cutworms, armyworms, several borers and other insect pests. Publication WO/EP97/07089 by Privalle et al. teaches the transformation of monocotyledons, such as corn, with a recombinant DNA sequence encoding peroxidase for the protection of the plant from feeding by corn borers, earworms and cutworms. Jansens et al., in Crop Sci., 37(5):1616-1624 (1997), reported the production of transgenic corn containing a gene encoding a crystalline protein from Bacillus thuringiensis that controlled both generations of the European corn borer. U.S. Pat. Nos. 5,625,136 and 5,859,336 to Koziel et al. reported that the transformation of corn with a gene from B. thuringiensis that encoded for delta-endotoxins provided the transgenic corn with improved resistance to European corn borer.
A comprehensive report of field trials of transgenic corn that expresses an insecticidal protein from B. thuringiensis has been provided by Armstrong et al., in Crop Science, 35(2):550-557 (1995).
At the present state of plant cellular engineering, however, transgenic crops are typically resistant only to specific pests for that crop, e.g., transgenic corn expressing a Bt toxin against the corn rootworm. It is frequently necessary to apply synthetic pesticides to such transgenic plants to control damage by other pests.
Insecticides such as synthetic pyrethroids, organophosphates and carbamates; fungicides such as azoles and anilopyrimidines; and acaricides such as pyrazoles; and the like, are very effective against certain above ground plant pests when applied at the proper time and with proper procedures. Appropriate pesticides may be applied at the time of planting as surface bands, “T”-bands, or in-furrow, but these applications require the additional operation of applying the pesticide at the same time as the seeds are being sown. This complicates the planting operation and the additional equipment required for pesticide application is costly to purchase and requires maintenance and attention during use. Moreover, care must be taken to incorporate the pesticides properly into the topmost soil layer for optimal activity. (See, for example, the application requirements and precautions for use of tefluthrin that are described in the brochure titled Force 3G Insecticide, published by Zeneca Ag Products, Wilmington, Del. (1998)).
The activity of pesticides that have been applied as in-furrow applications at the time of sowing is usually directed to the protection of the seed or the roots of the plant. Some protection against above ground pests such as corn borers has been reported, however, for such treatments with insecticides known to be systemic. Keaster and Fairchild, J. Econ. Entomol., 61(2):367-369 (1968). Since such pesticide chemicals are complex molecules that are expensive to produce, purchase and use, it is desirable that their activity is not diluted or lost by migration away from the desired site of action by moisture seepage or by vaporization.
After the plant has emerged from the soil, foliar spraying of pesticides is most often used to control those pests that attach the shoots and foliage of the plant. However, a foliar spray must be applied at a certain time that coincides with the presence and activity of the pest in order to have the most beneficial effect. Application at this time may be difficult or impossible if, for example, weather conditions limit access to the field. Moreover, the plants must be monitored closely to observe early signs of pest activity in order to apply the pesticide at a time when the pests are most vulnerable.
Synthetic pyrethroids have been found to give excellent control of pests of the order of Lepidoptera, such as cutworms, when applied as foliar spray or as surface-incorporated granules at the time of planting. However, since this class of insecticides has very high toxicity to fish, for example, great care must be taken to limit the runoff of the insecticide from either granules or spray into surface waters. Moreover, any foliar spraying must be done at times when there is little wind, and then only with proper equipment that is carefully monitored during use.
It has also been found in some cases with particular pesticides and application techniques that when two or more of such pesticides are used in particular combination greater efficacy results than when any one of such pesticides is used alone. Such benefits of combining pesticides has been reported for combinations of phosmet with diflubenzuron (U.S. Pat. No. 4,382,927); O-ethyl-O-[4-(methylthio)-phenyl]-S-propyl phosphodithioate and N′-(4-chloro-o-tolyl)-N,N-dimethylformamidine (U.S. Pat. No. 4,053,595); bacillus thuringiensis and chlordimeform (U.S. Pat. No. 3,937,813); decamethrine and dichlorvos with propoxur, if desired, (U.S. Pat. No. 4,863,909); fenvalerate and phosmet (U.S. Pat. No. 4,263,287); and phosalone and malathion (U.S. Pat. No. 4,064,237). However, each of these combinations was applied directly to the growing plant as described above in the form of sprays or dusts, or applied to the soil around the plant in the form of, for example, granules.
WO9740692 discloses combinations of any one of several oxadiazine derivatives with one of a long list of other insecticides. Although the application mentions that the combinations can be applied to plant propagation material for its protection, as well as to plant shoots and leaves, no examples are provided to demonstrate that any one of the combinations listed is actually efficacious. More pesticide combinations are described in U.S. Pat. Nos. 4,415,561, 5,385,926, 5,972,941 and 5,952,358. However, in the existing art, little or no guidance has been found as methods for predicting which combinations of pesticides will result in such unexpectedly superior efficacy and which combinations will not.
The control of pests by applying insecticides directly to plant seed is well known. For example, U.S. Pat. No. 5,696,144 discloses that the European corn borer caused less feeding damage to corn plants grown from seed treated with a 1-arylpyrazole compound at a rate of 500 g per quintal of seed than control plants grown from untreated seed. In addition, U.S. Pat. No. 5,876,739 to Turnblad et al. (and its parent, U.S. Pat. No. 5,849,320) disclose a method for controlling soil-borne insects which involves treating seeds with a coating containing one or more polymeric binders and an insecticide. This reference provides a list of insecticides that it identifies as candidates for use in this coating and also names a number of potential target insects. However, while the U.S. Pat. No. 5,876,739 patent states that treating corn seed with a coating containing a particular insecticide protects corn roots from damage by the corn rootworm, it does not indicate or otherwise suggest that treatment of corn seed with any particular combinations of insecticides provides the seed or the plant with synergistic protection, or with any other unexpected advantage.
Thus, although the art of protecting the shoots and foliage—as well as the seed and roots—of a plant from damage by pests has been advancing rapidly, several problems still remain. For example, it would be useful to provide a method for the control of pest damage to shoots and foliage of plants without the requirement of applying a pesticide at the time of sowing the seed, either as a surface incorporated band, or in-furrow, for example, or requiring a later field application of a pesticide during plant growth. It would also be useful if the method for pest control reduced the amount of pesticide that was required to provide a certain level of protection to the plant. Furthermore, it would be useful if such a method could be coupled with the biopesticidal activity of transgenic plants, or with the insecticidal activity of other active materials to provide a broader scope of protection than is provided by the transgenic elements, or the insecticidal actives alone.